600 



INVERTEBRATE MORPHOLOGY. 



upon the inner surface of which there is on each side a collar- 

 pore. 



The mouth (m) opens beneath the epistome into an oesoph- 

 agus, -which in the collar region bears a dorsal diverticulum, 

 the notochord {x), projecting forwards into the epistome. In 

 this same region there is on each side a branchial slit {sp), 

 structures which are apparently wanting in Rhahdopleura. 

 Behind the oesophagus opens into a saclike stomach from 



Fig. 273. — Diagrammatic LoNGiTUDiNAii Section through Oephalodiscus 

 (after Ehlers from Korschelt and Heider). 

 a = anus. n = nervous system. 



ex = excretory organ, sp = branchial slit. 



g = ovary. i = tentacles. 



m = mouth. x = notochord. 



which the intestine, bending upon itself, passes forwards to 

 open (a) upon the dorsal surface of the visceral sac, a short 

 distance behind the collar. 



The collar-pores probably serve as excretory organs, and 

 it has been stated that the epistome-pores open into well- 

 developed tubes (ex) terminating in the epistome cavity in a 

 dilatation ; they also have been regarded as excretory. The 

 reproductive organs {g) are paired sacs, which open on the 

 dorsal surface just in front of the anus. No circulatory system 



